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Learn how to effectively manage concurrent requests in your .NET Core Web API by using `SemaphoreSlim` to restrict the number of concurrent threads to 200, ensuring efficient API integration.
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How to Use SemaphoreSlim to Limit Concurrent Requests to 200 in .NET Core

Handling multiple requests efficiently is a vital aspect of developing robust APIs. In scenarios where you interact with third-party services that enforce request limits, it becomes crucial to institute proper concurrency control. This guide will guide you through the process of using SemaphoreSlim in your .NET Core Web API to limit concurrent requests to 200. We will explain the problem, provide an in-depth solution, and ensure that your application runs smoothly even under heavy load.

Understanding the Problem

In your .NET Core Web API, you may encounter situations where you need to call a third-party API that allows a maximum of 200 concurrent requests. However, if your application receives multiple requests from users simultaneously, the third-party API can throw errors due to overwhelming requests.

The challenge is to ensure that your application only allows up to 200 concurrent calls to this API, even across multiple user requests. This issue is common in high-traffic applications, and it's essential to implement it correctly using SemaphoreSlim.

The Solution: Using SemaphoreSlim Effectively

1. Define SemaphoreSlim Properly

The current implementation creates a new instance of SemaphoreSlim for every request. This approach means each request can have its own limit of 200 concurrent accesses, which does not truly limit the total requests across all active sessions. To solve this:

Declare your SemaphoreSlim as a static instance or inject it as a singleton.

This way, any active request will use the same SemaphoreSlim instance and adhere to the overall limit of 200.

2. Implementation Example

Here’s how you could revise your existing code to implement the solution:

[[See Video to Reveal this Text or Code Snippet]]

3. How the Code Works

Static Instance: By declaring the SemaphoreSlim as a static variable, it will manage a state shared across all requests.

Task Execution: When processing search criteria, only 200 tasks can be in progress simultaneously.

Error Handling: Each task handles its search call, and in case of an error, an appropriate message is logged.

Concurrent Management: The semaphore's release mechanism ensures that once a task completes, threads waiting to enter the block are notified, keeping your API within the request limits.

Conclusion

By restructuring your SemaphoreSlim instance to be shared between requests, you can effectively limit concurrent calls to a third-party API to a maximum of 200. This approach will not only help you avoid errors from overloading the API but also ensure a smoother experience for your users. Implementing good concurrency control is key in building reliable and efficient web applications.

By following the steps outlined above, you’re well on your way to mastering concurrency in your .NET Core applications. If you have any further questions or require additional examples, feel free to ask.